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ATCOLORADO <br />Division of Reclamation, <br />Mining and Safety <br />Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />Date: March 11, 2015 <br />To: Eric Scott, Division of Reclamation, Mining and Safety <br />From: Peter Hays, Division of Reclamation, Mining and Safety <br />Re: Second Review of Slope Stability Analysis, VESCO Consulting Services, LLC, GoodMiller <br />#2 Pit, File No. M- 2014 -070 <br />The Division of Reclamation, Mining and Safety (Division) staff has reviewed the stability <br />analysis dated March 9, 2013 submitted in response to the Division adequacy letter for the <br />GoodMiller #2 Pit permit application. <br />The following list describes the information used by the Division as presented in the revised <br />permit application geotechnical stability exhibit to evaluate slope stability for the site. <br />• A minimum 30 foot buffer will be maintained from the permit boundary line to all <br />excavations. <br />• The side slopes will be mined at a 1.6H:1V and reclaimed at 3H:1V. <br />• The maximum depth excavated will be 40 feet. <br />• No laboratory strength tests were performed on soils at the site. <br />• The soil strength parameters used were based on typical values for anticipated soils. <br />• Soils on the site are classified as GC (clayey gravels, poorly graded gravel- sand - clay). <br />• An analysis was performed using the formula; Factor of Safety (FOS) = Tangent of <br />Internal Angle of Friction / Tangent of Actual Angle of Failure Surface. Using a friction <br />angle of 31 degrees and a 20 degree slope angle, a 1.65 factor of safety was calculated. <br />• Groundwater was not accounted for in the stability analysis. <br />• The closest structure to the mine excavation limit is a power line 30 feet from the <br />excavation limit. No surcharge loading was included for the power line pole. <br />• Bedrock will not be exposed on the pit floor. <br />The Division verified the Applicant's stability analysis model using Clover Technology's Galena <br />v6.1 slope stability software. <br />—c <br />I he J \ o <br />1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http: / /mining. state. co. us * * <br />John W. Hickentooper, Governor I Mike King, Executive Director I Virginia Brannon, Director * 1876 -* <br />